0000000000585897
AUTHOR
J. H. Hamilton
New subshell closure atN=58emerging in neutron-rich nuclei beyondNi78
The structure of neutron-rich nuclei beyond $^{78}\mathrm{Ni}$ was studied using postaccelerated radioactive beams of $^{83,84,85}\mathrm{Ga}$ utilizing $\ensuremath{\beta} \ensuremath{\gamma}$ and $\ensuremath{\beta}\ensuremath{-}n \ensuremath{\gamma}$ spectroscopy. Our data, when combined with energy level systematics, suggests a possible new spherical subshell closure at $N=58$ is created by the nearly degenerated $\ensuremath{\nu}3{s}_{1/2}$ and $\ensuremath{\nu}2{d}_{5/2}$ orbitals being well separated from other orbitals above $N=50$. The near degeneracy of these states could be evidenced by isomerism in this region. The energies of the ${2}_{1}^{+}$ and proposed ${4}_{1}^{+}$ states …
Ca48+Bk249Fusion Reaction Leading to ElementZ=117: Long-Livedα-DecayingDb270and Discovery ofLr266
The superheavy element with atomic number Z=117 was produced as an evaporation residue in the 48Ca+249Bk fusion reaction at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. The radioactive decay of evaporation residues and their α-decay products was studied using a detection setup that allowed measuring decays of single atomic nuclei with half-lives between sub-μs and a few days. Two decay chains comprising seven α decays and a spontaneous fission each were identified and are assigned to the isotope 294-117 and its decay products. A hitherto unknown α-decay branch in 270Db (Z=105) was observed, which populated the new isotope 266Lr (Z=103). The identification of the long-liv…
Shell structure beyond the proton drip line studied via proton emission from deformed 141Ho
Abstract Fine structure in proton emission from the 7 / 2 − [ 523 ] ground state and from the 1 / 2 + [ 411 ] isomer in deformed nucleus 141Ho was studied by means of fusion-evaporation reactions and digital signal processing. Proton transitions to the first excited 2+ state in 140Dy, with the branching ratio of I p g s ( 2 + ) = 0.9 ± 0.2 % and I p m ( 2 + ) = 1.7 ± 0.5 % , were observed. The data are analyzed within the non-adiabatic weak coupling model assuming a large quadrupole deformation of the daughter nucleus 140Dy as predicted by the self-consistent theory. Implications of this result on coexistence effects around N = 74 are discussed. Significant modifications of the proton shell…
Search for elements 119 and 120
A search for production of the superheavy elements with atomic numbers 119 and 120 was performed in the 50Ti+249Bk and 50Ti+249Cf fusion-evaporation reactions, respectively, at the gas-filled recoil separator TASCA at GSI Darmstadt, Germany. Over four months of irradiation, the 249Bk target partially decayed into 249Cf, which allowed for a simultaneous search for both elements. Neither was detected at cross-section sensitivity levels of 65 and 200 fb for the 50Ti+249Bk and 50Ti+249Cf reactions, respectively, at a midtarget beam energy of Elab=281.5 MeV. The nonobservation of elements 119 and 120 is discussed within the concept of fusion-evaporation reactions including various theoretical pr…
Anomalous Behavior of High-Spin States inCm248
The ground-state band of $^{248}\mathrm{Cm}$ has been studied up to spin ${28}^{+}$ and tentatively to ${30}^{+}$ by observing $\ensuremath{\gamma}$ rays following multiple Coulomb excitation with use of $^{208}\mathrm{Pb}$ ions at 5.3 MeV/u. A smooth, gradual increase in the effective moment of inertia is seen at lower spin with an anomalous forward bend above spin ${22}^{+}$. Calculations are presented which indicate that this behavior including the forward bend can be understood in terms of the alignment of single-particle angular momenta along the rotation axis.
Fusion reaction Ca48+Bk249 leading to formation of the element Ts ( Z=117 )
The heaviest currently known nuclei, which have up to 118 protons, have been produced in 48Ca induced reactions with actinide targets. Among them, the element tennessine (Ts), which has 117 protons, has been synthesized by fusing 48Ca with the radioactive target 249Bk, which has a half-life of 327 d. The experiment was performed at the gas-filled recoil separator TASCA. Two long and two short α decay chains were observed. The long chains were attributed to the decay of 294Ts. The possible origin of the short-decay chains is discussed in comparison with the known experimental data. They are found to fit with the decay chain patterns attributed to 293Ts. The present experimental results confi…
117番元素Ts合成のための48Ca+249Bk融合反応
We have performed an experiment to synthesize the element 117 (Ts) with the $^{48}$Ca+$^{249}$Bk fusion reaction. Four $\alpha$-decay chains attributed to the element 117 were observed. Two of them were long decay chains which can be assigned to the one originating from the $\alpha$ decay of $^{294}$Ts. The other two were short decay chains which are consistent with the one originating from the $\alpha$ decay of $^{293}$Ts. We have compared the present results with the literature data, and found that our present results mostly confirmed the literature data, leading to the firm confirmation of the synthesis of the element 117.